In Praise of Fish Oil

Fish oil is an important part of Paul B's fish feeding regimen

Fish oil is an important part of Paul B’s fish feeding regimen

Hobby pioneer Paul “Paul B” Baldassano has some strong opinions on what types of foods are best for fish, formed over his many decades of involvement in the marine aquarium hobby. Somewhere near the top of his list is fish (or krill) oil.

From Chapter 3: Keeping Fish Healthy

Oil, in my opinion, is one of the most important things you can feed to fish. No, not Oil of Olay or olive oil, but fish or krill oil. I take it myself every day, but not too much, as I don’t want to resemble my old flounder-faced girlfriend.

In the sea, fish get a large percentage of their diet from pure fish oil. How do I know? Glad you asked. I have been scuba diving since 1970, when I did my first dive on the Great Barrier Reef in Australia. I was on R&R from Vietnam, and I met a girl there who took me to this restaurant where they give you all the dive equipment and throw you in the water. All you had to do was give them any extra fish you speared.

I caught an anemic-looking lobster, and she had a belt full of fish. When we surfaced and started back to shore, I heard machine gun rounds. I knew that sound because a couple days before, I was in a war. I said (not very calmly, I am sure), “What the hell is that?” She replied, “Don’t worry, they are shooting the sharks.” Apparently, sometimes a large shark gets tangled up in this net they have around the harbor, and they shoot it. I understand that there are holes in that net large enough to allow a tractor trailer to “swim” through, and the girl I was swimming with had a belt full of bleeding fish. To this day, that was the fastest I have ever swum.

Anyway, since then I have been diving all over the place and have spent about 200 hours under water. If you’ve done any real diving—the kind where you lie on the bottom by yourself until you run out of air or realize you forgot to remove your cell phone from your Speedo—you may have noticed schools of tiny fish fry, mostly near the substrate. Well, fish fry are like fast-food restaurants for most of the fish on a reef and form a large part of their daily diet. If you watch fish long enough, you will see them dip down often for a snack of fresh fish fry.

All fish have a liver. That liver serves a couple of functions besides cleaning the blood. It also helps with buoyancy, but only slightly in most fish. In sharks, the liver provides all of the buoyancy. Without the oil in their liver, sharks would swim about as well as Paris Hilton’s dog or a cinder block. In fact, the liver is mostly oil and can be 15% of the fish’s weight—almost 20% in sharks.

So think about this: When a fish eats another whole fish, it’s getting almost 15% of its diet as pure fish oil. If a shark eats a 100-pound grouper, it’s getting about 12 pounds of oil. That’s a lot of oil!

Check out the ingredients on a package of dry food and see if there is any oil. Oil doesn’t dry very well, and boy does it stink! So my theory is that fish require a large portion of their diet as oil. It makes sense to me and to the fish.

Also consider that in pregnant fish, the eggs can be almost a third of the weight of the fish, and those eggs are mostly oil. It is a huge burden on a fish to produce those eggs, and many of the correct extra calories are needed to do so. Just imagine how much a woman would have to eat in order to have a 50-pound baby every month!

So where can we get this oil? The best place is in whole fish, but whole tiny fish are not available live or frozen, and I don’t know why. (Tip to fish food manufacturers: Sell tiny frozen fish fry for food!) Fish and krill oil is also sold in capsules, and if I plan to feed my fish flakes or pellets, I always put a drop of fish oil on it first. Pellets soak up oil very well. However, don’t put oil of any kind on wet foods, such as frozen food, as it will just wash off as soon as the food hits the water.


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About Jeff Kurtz

Jeff Kurtz is the Co-founder/Editor of Saltwater Smarts, former Senior Consulting Editor for Tropical Fish Hobbyist Magazine, and the aquarist formerly known as “The Salt Creep.” He has been an aquarium hobbyist for over 30 years and is an avid scuba diver.


  1. I have been using fish oil as a supplement for years for the exact reasons Paul does. I also make my own foods and feed dry foods only once a day out of the four feeds I feed each day that is. I tell lots of people about fish oil and how I make my own foods but few people listen as like Paul I am nuts it seems. Apparently I am going to wipe my fish out using all these fresh or frozen ingredients as they have not been gamma irradiated or processed till the nutrition has all but left them.

    My fish live L O N G lives, most breed in my tank never get something called white spot whatever that is Oh! and I have never quarantined a fish in my life. See I told you I am nuts and just lucky I guess. I have been keeping marines for only a short period about 35 years so I still have a bunch of stuff to learn. I do feed stuff like frozen lobster and oyster eggs as I figured it’s a whole lot cheaper than travelling many miles and investing in scuba gear to go get them myself.

    Keep on doing what your doing Paul and taking those BIG risks like myself.

  2. Les, it is a shame that our tanks will crash shortly due to our practices of not quarantining and feeding fish oil to fish. What a stupid Idea. Of course feeding them popcorn, chicken McNuggets or God Forbid, flakes must be a much better idea. I really hate it when all my fish spawn because they get fat and are not as streamlined. I also hate it when I add a fish and it lives for 20 years, I mean, I get so tired of looking at it. Some day the rest of the people in this hobby will understand the little nuances that allow us to be able to talk like this as we both know it is so simple and probably cheaper that the norm. That is one reason I wrote a book. The other reason is that I want a Pulitzer. My book tries to bring back the simple, old school practices that we learned through trial and error by keeping fish for a very many years. We have gotten to the point now where our fish worry about our health rather than us worrying about them.

  3. Les Melling says

    Well Paul, we are so wrong it hurts me to say it. I tried feeding my fish the cornflakes most do but they just look at me and say “are you kidding me, get out of here and bring me some real food punk” Well I figured long ago it’s futile to argue with them. I tried telling them the junk food I was feeding them would catch up with them one day but they just keep on defying me and living long lives just to spite me of course.

    I once read what was on a famous tub of dried food and it scared the hell out of me and my fish. A lot of it was made from something called fishmeal and a load of E numbers. Unfortunately or is that fortunately my fish don’t read so well (I guess it must be the goldfish effect) and wouldn’t know an E number from one of your supper models Paul only I guess they wouldn’t really want to eat either.

    I might try them on some turkey at Christmas and even some Christmas pud but they might not want to eat it till your thanksgiving, We don’t have that here, we just have a queen and other nonsensical stuff to make us eat more than we can chew. I happen to mention the other day to a fellow aquarist that we can’t improve on nature, after all nature has had millions of years to perfect the perfect fish foods and if you try to mimic nature you wouldn’t go far wrong. I don’t think he quite got my message, no change there then hey? . .

  4. My fish like food with no more than one ingredient in it like worm, clam, fish, etc.

  5. Paul/Les
    Quick question just to clarify…
    Fish oil… Nothing fancy just plain fish oil like the gel capsules you buy at Walmart?
    Also the foods you recommend using this one would not be frozen or even a store bought flake?
    How much oil per serving?
    Thanks for your time and effort in the hobby

  6. I use fish oil capsules but drain the oil into the food and discard the capsule. I’m in the UK we don’t have Walmart but I would guess they are similar if not the same. I simply add one capsule to enough defrosted food for the day and allow the oil to soak into the food for around 20 mins giving it a good stir every now and then. You may find not all the oil is absorbed depending on what food you are adding it too but that is not a problem.

  7. I add it to sinking pellets, let it soak in for an hour or it will make an Exxon oil slick on your water. I would not feed dry food if I did not first add some oil. I put about 20 pellets into a dry container and add a drop or two of oil, then shake it around a little.

  8. I’ve got to do this from now on and save those decades from avoidable errors.
    Thank you. Cheers.

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